Alpha-hydro-gamma-hydroxy poly(oxymethylenenitroamino)polymer

ABSTRACT

A NOVE BINDER FOR PROPELLANT COMPOSITIONS, AND ITS METHOD OF PREPARATION, SAID BINDER BEING A POLYMER OF THE FORMULA:   H-(O-CH2-N(-NO2)-CH2-CH2-N(-NO2)-CH2-O-CH2-CH2)N-OH,   AND NOVEL PREPELLANT COMPOSITIONS THEREOF.

ABSTRACT OF THE DISCLOSURE A novel binder for propellant compositions, and its method of preparation, said binder being a polymer of the formula:

11- O CHzNCHr CHQNCHI O CHJCHg O H,

\ 1'... No. l.

and novel propellant compositions thereof.

BACKGROUND OF THE INVENTION Solid propellants are usually made of the three basic ingredients: (1) oxidizer, (2) fuel, and (3) binder. Two or even three of these may be contained in the same material. A convenient Way to divide solid propellants into classes is according to physical state, i.e., homogeneous (single-base or double-base) and composite. A single-base propellant contains nitrocellulose as the main ingredient with a stabilizer such as diphenylamine added, as well as other conventional additives depending on the application. Single-base propellants are used primarily in gun applications and cartridge-actuated devices. Double-base propellants have two principal ingredientsnitrocellulose and nitroglycerine, and may have various conventional ingredients as stabilizers, burning rate modifiers, extrusion lubricants and flash suppressors. When additional oxidizers are added to the double-base propellant, one has a composite modified double-base propellant. Composite propellants are generally composed of an oxidizer and a fuel and/or binder. Well-known oxidizers and fuels are used.

The binder material in composite propellants usually is a polymeric material and nitrocellulose is the most commonly known and used binder component. Thus, nitrocellulose finds wide use in all types of propellant formulations. However, the use of nitrocellulose as a binder in gun propellants results in a high flame temperature and low gas output, both of which are undesirable features. While the replacement of nitrocellulose in gun propellants with a rubber binder gives better flame temperature and gas output, it requires large amounts of output for efiicient propellant combustion. Moreover, in solid rocket propellants and other composite propellants, while nitrocellulose ofiers high energy it generally gives poor low temperature mechanical properties and relatively high sensitivity. The use of a rubber binder for these composite propellants improves the low temperature mechanical properties and sensitivity but such propellants are less energetic and less efficient than those based on nitrocellulose.

' United States Patent 3,808,276 Patented Apr. 30, 1974 SUMMARY OF THE INVENTION It is an object of this invention to obtain a new binder for propellant compositions, and a method of preparing such a binder.

It is an additional object of the instant invention to obtain a new binder for propellant compositions which has a low flame temperature.

It is a further object of the present invention to obtain a new binder for propellant compositions with a high gas output.

It is still another object of the instant invention to produce propellant compositions which have good low temperature mechanical properties.

It is yet another object of the instant invention to produce a propellant having low sensitivity.

It is still another object of the invention to produce a binder for propellant compositions which is thermally stable.

Still another object of the instant invention is to produce a binder for propellant compositions which is compatible with other propellant ingredients.

It is an additional object of the present invention to produce a binder for propellant compositions which can be used as a replacement for or additive to a nitrocellulose binder.

These and other objects are accomplished by the use of a new polymer binder which offers the desirable advantage of both nitrocellulose and rubber binders, in solid propellants such as gun propellants and rocket propellants.

The objects, advantages, and novel features of the invention will become apparent from the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The novel binder polymer of the instant invention is a-hydro-w-hydroxy poly (oxymethylenenitramino),

and is designated as EDNAP. While any molecular weight polymer will sufiice so long as the polymer is operable for binder purposes, it is preferred to use a polymer of a molecular Weight of from about 750 to about 3000, or more preferably from about 1000 to about 2500. This type of polymer is synthesized by reacting 1, 6-dichloro- 2,5-dinitrazahexane (DCDNH) with a polyhydroxy alcohol, exemplified by ethylene glycol. The polymer is thermally stable and can be crosslinked with hexane diisocyanate to form a rubbery gumstock.

A more detailed description of the preparation is as follows. The DCDNH, which reacts with the polyfunctional alcohol, is prepared by reacting ethylene dinitramine with formaldehyde and hydrogen chloride in acetic acid at about 0 C. The DCDNH is usually recrystallized from benzene before preparing the polymer. The bulk reaction between DCDNH and the poly-o1 may be carried out between room temperature and C., but the range of 40-60 C. is preferred. The ratio of hydroxyls to chlorines in the respective reactants may be 1.0 to 1.3. Operation under reduced pressure is desirable so as to rapidly remove the hydrogen chloride generated by the reaction and thereby prevent its reaction with the poly-o1.

TABLE I Nitrocellulose Butarez EDNAP (12.6%) H Empirical formula CeHizN40t csHmzNmtOo-n 1 AHr, kcal./l g .4 -58. 8 6.7 Monopro ellant, impetus 273,000 375,000

(it-lbs. 1b.). Flame temperature K).-. 1,800 3,435 Gas output, moles/100 g- 5.4 4.0 Density, g./cc 1.36 1.66 0.90

1 Butarez is not a monopropellant.

The low flame temperature and high gas output of EDNAP is ideal for gun propellant applications. For example, propellants with about 20% EDNAP as a binder with other Well-characterized compounds have a calculated impetus of up to 420,000 ft.-lb./lb. at 2700 K. This is a 25% gain over Olin ball powder which is presently used for many gun propellant applications.

In solid rocket propellants EDNAP also calculates well. For example, Table II shows two formulations which are comparable to composite modified double-base (CMDB) propellants in impulse. The advantages of the EDNAP binder rocket propellants are their expected good low temperature mechanical properties and lower sensitivity compared to the CMDB propellants.

TABLE II Percent composition I Densit Jcc 1. 895 1. s52 LDP- g 505 505 or, 0. 255 0. 028

In use in solid propellants, the cured polymer is generally used. The polymer can be cured with any conventional curing agent such as any of the crosslinking polyfunctional isocyanates. Exemplary are toluene diisocyanate and hexane diisocyanate, to name just a few of the many conventional crosslinking agents readily available. A wide variety of propellant compositions can be made using the cured prepolymer as the binder. It is preferred to use the EDNAP in double-base and composite type propellants, rather than in single-base propellants. In a composite propellant the amount of EDNAP present is about 10-25 percent by weight of the propellant composition. In these composite types, conventional fuels, such as aluminum, beryllium, zirconium, magnesium, boron, and their corresponding hydrides, as well as lithium, and lithium aluminum hydride, may be used in amounts varying from 0 to 25 percent by weight, preferably at least about 10 percent by weight. Conventional oxidizers, such as cyclotetramethylenetetranitramine (RDX), and ammonium and alkali metal nitrates or perchlorates may be present in amounts ranging from about 55 to 90 percent. With respect to the latter, it would be preferable to have from 55 to 80 percent of oxidizer because it is desired to have at least 10 percent of fuel present in the composition, although the propellants would be operative in the absence of the fuels. In addition to the oxidizer, EDNAP and fuel, any of the conventional additives such as plasticizers, curing agents, stabilizers, burning rate additives, catalysts, etc., are also possible components of the composite formulation. The amount of curing agent necessary to crosslink the polymer is not critical and generally conventional amounts of about 1 to about 6 percent will sufiice. With respect to the amount of plasticizer present, usually the EDNAP may be plasticized with up to twice its weight with energetic materials like nitroglycerine or diethylene glycol dinitrate.

In a double-base type propellant, a satisfactory propellant can be obtained by replacing up to about one half of the nitrocellulose with EDNAP. Thus, while the typical double-base propellant will contain about 30-50 percent by weight of a high energy explosive such as nitroglycerinc diethylene glycol dinitrate, methyl trimethylolmethane trinitrate or others, and about 40 to about 60 percent of nitrocellulose, the propellant compositions of the instant invention will contain from about 1 to about 30 percent of EDNAP, replacing up to about one half of said nitrocellulose, usually present in the conventional type. The resulting propellant will have the polymer present in an amount equal to or less than the amount of nitrocellulose present. Conventional additives, such as plasticizers (phthalates, triacetin, etc.), stabilizers (Z-nitrodiphenylamine, tertiary butyl catechol, etc.), burning rate modifiers (lead salts, etc.), extrusion lubricants (stearates, soaps, etc.), and flash suppressors (potassium salts, etc.) may also be added.

The following examples illustrate the method of obtaining the novel polymer as well as some propellant formulations utilizing the novel polymer.

EXAMPLE I 0.6 mole of DCDN'H, 0.56 mole of ethylene glycol, and 0.11 mole of glycerol were reacted at 50-60 C. for 24 hours at the low pressure level produced by a water aspirator. The cooled reaction mixture was dissolved in methylene chloride and washed successively with water, sodium bicarbonate solution, and finally sodium hydroxide solution. For drying, benzene was added to the solution and the total solvent was distilled. Last traces of solvent were removed by sparging with dry nitrogen at 60 C. The product, on analysis, was found to contain 0.19% water and to have an hydroxyl equivalent weight of 572.

EXAMPLE II A propellant formulation was prepared in the laboratory of the following composition:

Constituent: Percent by weight Aluminum l2 HMX 65 EDNAP 19.2 HDI (hexamethylene diisocyanate) 3.8

This composition has a calculated specific impulse of 265 seconds and a density of 0.065 lb./in. Its burning rate of 1000 psi. was 0.21 in./sec.

EXAMPLES III-IV wherein the molecular weight varies from about 750 to about 3000.

5 6 2. A polymer according to claim 1, wherein the 1110- OTHER REFERENCES lecular weight varies from about 1000 to about 2500. Wagner & look; Synthetic Organic chemistry References Cited LEWIS GO'ITS, Primary Examiner UNITED STATES PATENTS 5 D. R. PHILLIPS, Assistant Examiner 3,121,748 2/1964 Gey et al. 260-584 C US. Cl. X.R. 3,609,115 9/1971 Sammons et a1. 260-584 C 260 5 3 C, 534 C 2 149 88, 2 

